Suppose I've written code like: ```rust enum Foo { Bar { bar: u32 }, Baz, } fn is_bar(foo: &Foo) -> bool { match foo { &Foo::Bar { bar } => true, &Foo::Baz => false, } } ``` The `bar` variable is unused, and the error message I get looks like: ``` warning: unused variable: `bar` --> src/main.rs:37:21 | 37 | &Foo::Bar { bar } => true, | ^^^ help: consider using `_bar` instead | = note: #[warn(unused_variables)] on by default ``` The help is incorrect; `_bar` is invalid. It should suggest replacing `bar` with `bar: _`